Lead acid batteries are inexpensive and, due to their comparatively high battery voltage, can provide high power. Because of these features, they have been used in various applications. Lead acid batteries are required to reduce, as much as possible, their self-discharge and loss of water from electrolyte. In view of this, a lead-calcium alloy that does not contain antimony is used for a grid in positive and negative electrode plates because antimony increases self-discharge and loss of water. Adding tin to the lead-calcium alloy can enhance the corrosion resistance of the grid.
Conventionally, the grid for lead acid batteries has been produced, for example, by expanding a lead-alloy sheet obtained by continuous casting. Continuous casting is a process in which a molten lead alloy is poured into contact with a roll mold and solidified. It is known, however, that the lead-alloy sheet obtained by this process results in a double layer structure, due to the difference of the alloy structure between where the molten metal contacts the roll mold and where it contacts the air. A positive electrode grid obtained from such lead-alloy sheet does not have sufficient corrosion resistance and fatigue strength.
Patent Literature 1 discloses to produce a lead-alloy sheet by continuously extruding a lead alloy at a temperature 10 to 100° C. lower than its melting point, and then rolling the alloy while cooling slowly at a temperature 50 to 230° C. lower than the melting point.